1. Field of the Invention
The present invention generally relates to magnetic disk units, and more particularly to a magnetic disk unit which is constructed to read parameters that are set for each head from a system region or area on a magnetic disk and to store or develop the read parameters in a storage part.
2. Description of the Related Art
Characteristics of heads and magnetic disks vary for each head and each magnetic disk. For example, if the output differs for each head, it is necessary to change the gain of an automatic gain control (AGC) in a read channel (RDC) within a magnetic disk unit for each head. In addition, if the write performance differs for each head, it is necessary to change a write current of a head amplifier within the magnetic disk unit and a write precompensation of the read channel for precompensating a phenomenon in which the actual write position appears shifted from a target position. Furthermore, if the mechanical resonance characteristic differs from each head, it is necessary to change a notch filter characteristic of a servo system within the magnetic disk unit for each head.
Recently, due to the core width and the read write performances of the heads used, techniques generally employed in the magnetic disk unit vary the track per inch (TPI) and the data transfer rate. In this case, the TPI and the sector format information differ for each head, and for this reason, it is necessary to change the parameters to optimum parameters that are different for each head.
The parameters that are set for each head include parameters that depend upon the characteristics of the magnetic disk that corresponds to each head, and there are many kinds of parameters that are set for each head. Typical read parameters used at the time of the read include the read frequency, sense current of an MR head, AGC gain, filter cutoff frequency, boost of specific portion of the filter characteristic, constants of a FIR filter, vertical asymmetry correction of the reproduced waveform, and the like. In addition, typical write parameters used at the time of the write include the write frequency, write precompensation, write current, overshoot of the write current, and the like.
Accordingly, because the optimum parameters differ for each head, the parameter settings must be tabulated and stored in the storage part within the magnetic disk unit independently for each of the heads. The parameters for each head are prerecorded in the system region on the magnetic disk, and when the power of the magnetic disk unit is turned ON, the parameters are read from the system region and stored in the storage part within the magnetic disk unit as parameter tables for each of the heads. The parameters of the parameter tables are read from the storage part and used thereafter at the time of the read or write.
The parameters for each head are stored as the parameter table in the storage part within the magnetic disk unit and used, as described above. But in order to reduce the number of processes required to develop the firmware of the magnetic disk unit, the firmware is created so as to store the parameter tables at the same addresses of the storage part even when the number of heads used differ among the magnetic disk units. For example, in the case of a type of the magnetic disk unit capable of providing up to four heads at the maximum, a model having a storage capacity of 400 GB is formed by using the four heads, and a model of the same type but having a storage capacity of 100 GB is formed by using one head. In this case, the model having the storage capacity of 100 GB may only be provided with one head or, provided with more than one head but set to use only one head. However, since the storage addresses of the parameter tables within the storage part are the same for the different models of the same type of magnetic disk unit, the parameter table corresponding to the one head that is set to be usable includes the parameters peculiar to this one head regardless of whether the magnetic disk unit is the model having the storage capacity of 400 GB or the model having the storage capacity of 100 GB, while the parameter tables corresponding to the three heads that are set to be non-usable are empty in the case of the model having the storage capacity of 100 GB. But in the model having the storage capacity of 100 GB, a storage region for storing the parameter tables corresponding to the three heads that are set to be non-usable is still reserved within the storage part of the magnetic disk unit.
In order to improve the performance of the magnetic disk unit, cache control techniques, such as the preread to a cache region of the storage part and a cache operation at the time of the write, are essential. In order to increase the effects of the cache control, it is of course preferable that the cache region is large, and a storage region that is not used at all prevents the improvement of the performance of the magnetic disk unit.
A Japanese Laid-Open Patent Application No. 2003-249044 proposes a magnetic disk unit that stores the parameters for each head in the storage part. The Japanese Laid-Open Patent Application No. 2003-249044 has a corresponding U.S. Pat. No. 6,781,786.
In the conventional magnetic disk unit using the firmware which stores the parameter tables at the same addresses within the storage part regardless of the number of heads (or the storage capacity) that are set to be usable, the storage region for the parameter tables are fixedly reserved within the storage part depending on the maximum number of heads that can be provided in the magnetic disk unit. For this reason, in the case of the magnetic disk unit that is set to use a number of heads smaller than the maximum number of heads that can be provided in this magnetic disk unit, the storage region for the parameter tables are reserved within the storage part with respect to the heads that are set to be non-usable and are actually not used. Consequently, there was a problem in that the usable (or available) storage capacity of the storage part becomes unnecessarily reduced.
As described above, there are many kinds of parameters that are set for each head. In addition, the write parameters used at the time of the write may be changed depending on the temperature, and thus, even for the same kind of parameter, the parameter table may include values that are different for each temperature, and the number of parameters increases considerably in such a case. Furthermore, even for the same parameter, the parameter table may include values that are different for each zone on the magnetic disk, and the number of parameters also increases considerably in such a case.
Recently, techniques have been proposed to provide a built-in heater in the head, and to improve the characteristics of the head by making the head project towards the magnetic disk by a driving current applied to the heater. In this case, the driving current applied to the heater is set for each head, and the driving current for each head is further set for each temperature and set also for each zone. Therefore, the number of parameters set for each head increases considerably in such a case.
Moreover, although the number of parameters set for each magnetic disk is smaller compared to the number of parameters set for each head, problems similar to those described above also occurred with respect to the parameters set for each magnetic disk.
Therefore, the storage capacity of the storage region within the storage part for storing the parameter tables is increasing with the increase of the number of kinds of parameters, and it is undesirable to reserve the storage region within the storage part for storing the parameter tables with respect to the heads that are set to be non-usable and actually not used and/or the magnetic disks that are set to be non-usable and actually not used.